It is said that the cure rate in cancer treatment is about 50%. at present, and generally, such cure is brought about often by topical therapy such as surgical therapy and radiotherapy. It is in a very low rate that chemotherapy as systemic therapy can contribute solely to cue, particularly in treatment of solid tumor, and usually chemotherapy is used in combination with various therapies.
On the other hand, surgical therapy enables surgery in every organ cancer and is considered to reach completion as therapy, and no further improvement in cure rate can be expected. The treatment results of susceptible organ cancers by radiotherapy also arrive at an almost fixed rate, and no further improvement in cure rate can be expected as well.
Accordingly, no significant improvement in cancer cure rate by these therapies can be expected in the future, and the development of further excellent chemotherapy is essential for further improving the cancer cure rate of 50% at present to arrive at cure for cancer.
An purpose of an anticancer agent used in chemotherapy lies in cytocidal effect on cells having a high ability to grow, such as cancer cells, and its damage to normal cells particularly myeloid cells having a high cellular growth ability is significant, and as a result, severe pain is given to patients. This is because the transfer of the anticancer agent is due to systemic administration by an injection, and the anticancer agent reaches normal cells other than cancer cells, so that the normal cells are killed and homeostasis does not function.
At present, however, the effect of an anticancer agent administered alone is regarded to be approximately about 30%, and it is expected that genetic information analysis and study on genome proceed so that selection of a suitable anticancer agent feasible can be expected in the future, but it is said that the therapy with the anticancer agent at present results in higher side effects.
This is because normal cells are damaged by systemic administration of an anticancer agent. Accordingly, if cancer tissue-specific delivery of the anticancer agent and subsequent incorporation thereof into cancer cells can be established, an ideal system of delivering the anticancer agent can be realized. In addition, if incorporation of the anticancer agent into a vesicle is feasible, a therapeutic method that is specific for target organ and cell with less influence (side effect) on normal cells can be established. Further, this can lead to reassessment of anticancer agents whose development was abandoned because of their strong side effects.